<template>
  <ul class="list">
    <li class="item" v-for='(item,key) in cities' :key='key' :ref='key' @click='handleLetterClick' @touchstart='handleTouchStart' @touchmove='handleTouchMove' @touchend='handleTouchEnd'>{{ key }}
    </li>
  </ul>
</template>
<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  data () {
    return {
      touchStatus: false
    }
  },
  methods: {
    handleLetterClick (e) {
      this.$emit('change', e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        const startY = this.$refs['A'][0].offsetTop
        const touchY = e.touches[0].clientY
        const index = Math.floor((touchY - startY) / 20)
        if (index >= 0 && index < this.letters.length) {
          this.$emit('change', this.letters[index])
        }
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}

</script>
<style lang='stylus' scoped>
@import '~styles/varibles.styl'

.list {
  display: flex;
  flex-direction: column;
  justify-content: center;
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  width: .4rem;
  text-align: center;
  padding-top: 1.2rem;
}

.item {
  line-height: .4rem;
  color: $bgColor
}

</style>
